1. Field of the Invention
The present invention relates to the vertical blanking interval (VBI) of TV signal, and more particularly, to an apparatus and method for detecting the vertical blanking interval of TV signal.
2. Description of the Prior Art
The vertical blanking interval (VBI) is a blank interval reserved in a TV signal for the attachment of all kinds of information. FIG. 1 shows the positions of scan lines for the VBI in different TV specifications. In the National Television System Committee (NTSC) system, each video frame has 525 scan lines; in the Phase Alternating Line (PAL) system, each video frame has 625 scan lines. FIG. 1 illustrates the scan line numbers for Closed Caption (CC), Copy Generation Management System (CGMS), Wildscreen Signaling (WSS), Video Programming System (VPS), and Teletext (TTX) 625B.
FIG. 2 is a schematic diagram of a typical VBI signal. As shown, the VBI signal contained in a scan line comprises the following portions: horizontal synchronization (Hsync) signal, color burst signal, clock run-in signal, frame code and data. Different VBI types correspond to different clock run-in signals and frame codes. A conventional VBI decoder is configured according to scan lines positions of a VBI signal within the TV signal. For example, VBI decoding is set to start when the scan line at a certain position is received. Further, for different scan lines containing different VBI signals, the conventional VBI decoder needs to respectively preset the parameters associated with each different VBI type in order to perform VBI decoding accurately.
Therefore, the conventional VBI decoder needs to know in advance which scan line position contains a VBI signal and which VBI type the VBI signal belongs to, and preset the associated parameters required for a subsequent VBI decoding process. Thus, the conventional VBI decoder is very inconvenient and inflexible for use.